Power measurement device

ABSTRACT

A power measurement device for sampling current or voltage signals of a power system to produce a 1-bit delta-sigma bitstream. The power measurement device includes a frequency locked loop for determining the power system frequency directly from the 1-bit delta-sigma bitstream. The frequency locked loop includes a 1-bit rotate CORDIC that is configured to produce difference signals having a multi-bit word for each bit of the 1-bit delta-sigma bitstream, and a phase error calculator that determines the difference between the phase of the power system frequency and a phase ramp generated from a frequency measurement value in a frequency register. The phase error calculator feeds back a phase correction signal to the frequency register to lock the frequency measurement value to the power system frequency.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a continuation of U.S. patent applicationSer. No. 13/024,211 filed Feb. 9, 2011.

FIELD

The present application generally relates to power system measurementsand monitoring and, in particular, to devices for synchronized phasormeasurements and transient capture and reporting.

BACKGROUND

Current efforts to improve power system monitoring and event reportingfocus upon detecting and correlating data from a number of dispersedsites in the network. To achieve synchronized readings, local datasampling is typically referenced to a time base synched to an absolutetime reference, such as can be obtained through the global positioningsystem (GPS). Measuring devices sample current and voltage values andmay perform some analysis on the data, such as harmonic analysis.Typical sampling rates may range from 1 to 12 kHz for high resolutionmeasurements, or 500 times that frequency (e.g. up to 6 Ms/s) for highspeed lower-resolution transient detection.

A typical power system measurement device uses separate circuits withdifferent sampling rates in order to accomplish high resolutionmeasurements and high speed transient capture. The use of two circuitsintroduces complexities for combining the data into a single useful datastream. The gain and aperture match between the two circuits cannot bemade perfect.

Typical power system measurement devices low pass filter sampled data toremove noise and other artefacts.

Accuracy, speed and low cost are desirable attributes in developing apower measurement device.

BRIEF DESCRIPTION OF THE DRAWINGS

Reference will now be made, by way of example, to the accompanyingdrawings which show example embodiments of the present application, andin which:

FIG. 1 shows a simplified block diagram of a power measurement device;

FIG. 2 shows a simplified example block diagram of the signal processorfrom the power measurement device of FIG. 1;

FIG. 3 shows a simplified example graph of the spectrum of a powersignal after delta-sigma modulation;

FIG. 4 shows a more detailed block diagram of an example signalprocessor;

FIG. 5 shows a simplified block diagram of a CORDIC-based implementationof a 1-bit FLL/PLL; and

FIG. 6 diagrammatically illustrates one example implementation of a1-bit rotate CORDIC; and

Similar reference numerals may have been used in different figures todenote similar components.

DESCRIPTION OF EXAMPLE EMBODIMENTS

In one aspect, the present application discloses frequency locked-loopfor locking to a system frequency of a signal sampled by a delta-sigmamodulator, wherein the delta-sigma modulator outputs a 1-bit delta-sigmabitstream. The frequency locked-loop includes a 1-bit rotate CORDIC thatreceives a phase ramp signal and the 1-bit delta-sigma signal andoutputs an in-phase difference signal and a quadrature-phase differencesignal, the difference signals each having a multi-bit word for each bitof the 1-bit delta-sigma signal, the phase ramp signal being derivedfrom a frequency value maintained by the frequency locked-loop.

In another aspect, the present application describes a power measurementdevice. The device includes a delta-sigma modulator configured to sampleone of voltage or current in a power system and output a 1-bitdelta-sigma bitstream, the voltage or current having a system frequency;a frequency locked-loop configured to receive the 1-bit delta-sigmabitstream and output a frequency value locked to the system frequency;and a transient capture module configured to receive the 1-bitdelta-sigma bitstream, filter selected spectra from the 1-bitdelta-sigma bitstream to obtain transient data.

In a further aspect, the present application discloses a powermeasurement device includes a delta-sigma modulator configured to sampleone of voltage or current in a power system and output a 1-bitdelta-sigma signal, the voltage or current having a system frequency;and a frequency locked-loop. The frequency locked-loop includes a 1-bitrotate CORDIC that receives a phase ramp signal and the 1-bitdelta-sigma signal and outputs an in-phase difference signal and aquadrature-phase difference signal, the difference signals each having amulti-bit word for each bit of the 1-bit delta-sigma signal, a phaseerror calculator configured to receive the difference signals and tooutput a phase error signal based upon the difference between a phase ofthe phase ramp signal and the phase of the system frequency containedwithin the 1-bit delta-sigma signal, a frequency register containing afrequency value, a phase accumulator configured to produce the phaseramp signal having a periodicity determined by the frequency value. Thefrequency locked-loop is configured to adjust the frequency value basedupon the phase error signal so as to lock the frequency value to thesystem frequency.

In yet a further aspect, the present application describes a method ofmeasuring power system characteristics, the power system having a systemfrequency and one or more phases. The method includes sampling one ofvoltage or current of the power system to produce a 1-bit delta-sigmabitstream; generating in-phase and quadrature difference signals fromthe 1-bit delta-sigma bitstream using a 1-bit rotate CORDIC receiving aphase ramp signal, wherein the phase ramp signal is based upon afrequency value; and locking the frequency value to the system frequencyby generating a phase error signal based upon a difference between aphase of the phase ramp signal and the phase of the system frequencycontained within the 1-bit delta-sigma signal, wherein the difference isobtained from the difference signals.

Other aspects and features of the present application will be understoodby those of ordinary skill in the art from a review of the followingdescription of examples in conjunction with the accompanying figures.

In the description that follows a number of simplifications are made forease of illustration. For example, those skilled in the art willappreciate that in many instances power measurement devices may beconfigured to measure three phases of voltage and current, whereas inthe embodiments described herein a single phase of voltage and/orcurrent may be illustrated for simplicity.

Reference is first made to FIG. 1, which shows a simplified blockdiagram of a power measurement device 10. The device 10 includes a 1-bitDelta-Sigma (DS) modulator 12 for measuring the power quantity (voltageor current on one of the phases) and producing a 1-bit signal orbitstream 14. The clocking of the DS modulator 12, and thus the bit rateof the output bitstream 14, may range from 10 KHz to 6 Ms/s, dependingon the resolution and frequency response required in the implementation.It will be understood that conventional DS converters employ a low-passfilter at the output to remove the high frequency quantization noisecomponents of the delta-sigma modulation. The device 10 does not employsuch low pass filtering but, instead, retains the high frequencycomponents as will be discussed and described further below. As notedabove, for simplicity a single DS modulator 12 is illustrated in FIG. 1.Practical implementations may have two or more DS modulators formeasuring current and voltage signals on one or more phases. In the caseof a three-phase three-wire system, six DS modulators may be used so asto measure current and voltage on all three phases. Similarly, in thecase of a three-phase four-wire system, eight DS modulators may be usedso as to measure current and voltage on all three phases and theneutral.

The device 10 further includes a time synch subsystem 16 that receivesan external time source signal. The external time source signal providesan absolute time reference and may be obtained from, for example, GPS oran IRIG-B signal. Other external signals may also serve as the absolutetime reference in some implementations. The time synch subsystem 16provides a clock correction signal or error signal 18.

The device 10 includes a signal processor 20. The signal processor 20receives the bitstream 14 and performs signal analysis and measurementsas described in greater detail below. In particular, the signalprocessor 20 is implemented to operate on the 1-bit DS output bitstream14 directly. The signal processor 20 receives the clock correctionsignal 18 for accurately correcting local oscillators (not illustrated).Rather than locking the local oscillators to the external absolute timereference signal, such as GPS, the time synch subsystem 16 provides acorrection factor in the form of the clock correction signal 18, whichin one implementation may provide up to a 100 parts per millioncorrection factor. The signal processor 20 may incorporate thecorrection factor from the clock correction signal 18 into afrequency/phase locked loop used to measure frequency and phase of thebitstream 14 signal, and thereby producing accurate synchronized phasor(synchrophasor) measurements. In other embodiments, the local oscillatormay be used more directly.

The signal processor 20 produces high accuracy synchrophasormeasurements of the power system fundamental. It may also selectivelydetect and measure phasors of harmonics present (selected by powercontent), perform transient detection, and perform residual waveformcapture.

The device 10 may include a memory or buffer 22 for storing measurementdata. It also includes a communication subsystem 24 for communicatingwith a remote location 30. The communication subsystem 24 may implementany of a variety of communication protocols and physical layerconnections. In one example embodiment, the communication subsystem 24may implement Ethernet (10/100 or Gigabit, for example), GSM, 802.11WiFi, USB, etc. In some implementations the communication subsystem 24may operate in accordance with two or more communication protocols.

FIG. 1 does not illustrate the data format used to transmit powermeasurements or analysis to the remote location 30 via the communicationsubsystem 24. The compression and encoding of data may be implemented bythe signal processor 20, the communication subsystem 24, or both. Insome example embodiments, data may be entropy encoded using a suitablelossless coding scheme, such as variable length coding (VLC), likeHuffman coding or arithmetic coding.

The signal processor 20 may be implemented in a number of ways. In someembodiments, the signal processor 20 may be implemented using a fieldprogrammable gate array (FPGA). In some embodiments, it may beimplemented using a suitable programmed general purpose microcontrolleror microprocessor. In yet other embodiments, it may be implemented usinga digital signal processor. In yet further embodiments, it may beimplemented using an application-specific integrated circuit (ASIC). Insome embodiments, the foregoing may be supplemented with discrete analogand/or digital components for implementing certain operations or aspectsof the signal processor 20. The full range of possibilities will beapparent to those of ordinary skill in the art in light of the followingdescription.

It will be appreciated that the simplified diagram shown in FIG. 1 omitsa number of components or elements that may be included in the device10, such as debugging circuitry, local oscillator circuitry for aninternal clock, isolation hardware, power source circuitry, etc.

Reference is now made to FIG. 2, which shows a simplified example blockdiagram of the signal processor 20. The one-bit DS bitstream 14 is inputto the signal processor 20. The signal processor 20 also receives thetime correction signal 18 (FIG. 1) and a local clock signal (not shown).

The signal processor 20 includes a 1-bit dual frequency locked-loop(FLL) and phase-locked-loop (PLL) 32 architecture. The 1-bit FLL/PLL 32outputs phasor data, such as a frequency signal 49 and a phase signal48. It will be understood that in the case of a polyphase system, theremay be multiple phase signals 48. It will also be understood that insome implementations more than one frequency signal 49 may be output,such as one signal measured from a voltage transformer signal, andanother from a current transformer signal. It may also be noted that insome embodiments it may be advantageous to have more than 1 FLL. Forexample, if the measurement device 10 (FIG. 1) were configured for useas a Synchro Check device to confirm that a new power generation sourceis at the correct phase before connection to the system.

The signal processor 20 further includes a 1-bit RMS calculator 34. TheRMS calculator 34 calculates the root-mean-square value of the input DSbitstream, thereby producing an RMS signal 42.

The signal processor 20 also includes a transient capture and phase jumpdetection component 36. The transient capture and phase jump detectioncomponent 36 is configured to detect possible transients in thebitstream 14. The transient capture and phase jump detection component36 may output a residual data signal 44 in some embodiments. Theresidual data signal 44 includes the noise data from the delta sigmamodulation. In this regard, the transient capture and phase jumpdetection component 36 may remove “significant” or “fundamental”components from the signal by spectral selection, leaving the residualcomponents. The residual data signal 44 contains these components. Insome embodiments, the transient capture and phase jump detectioncomponent 36 may output a transient detect signal 46. The transientcapture and phase jump detection component 36 may generate the transientdetect signal 46 by analyzing the residual data, for example usingspectral power analysis or another mechanism for detecting largemagnitude changes or fluctuations in the noise signal, and outputtingthe transient detect signal 46 in response to detection of possibletransient events in the residual data.

Reference is now made to FIG. 3, which shows a simplified example graph90 of the spectrum of a power signal after DS modulation, i.e. thespectrum of one of the 1-bit DS bitstreams 14. The graph 90 shows thatthe power system fundamental frequency is found at about 60 Hz, andthat, because the DS modulator pushes the quantization noise to higherfrequencies, less signal to noise ratio is available and more noise isencountered in the system at higher frequencies. In conventional powermeasurement, low pass filtering may be applied to remove the noisecomponent before phasor calculation and analysis; however, transientdata and other artifacts of interest may be found in the high frequencynoise. Accordingly, in accordance with an aspect of the presentapplication, phasor calculation and analysis is performed directly onthe 1-bit bitstream 14 without first low pass filtering the bitstream14.

Reference is now made to FIG. 4, which shows a more detailed blockdiagram of an example signal processor 20. The signal processor 20 inthis example includes a transform processor 50, such as a DiscreteWavelet Transform (DWT) or a Discrete Fourier Transform (DFT), whichproduces a transform domain signal 52 that represents the spectralcomponents found in the bitstream 14. The transform processor 50 mayalso be configured to produce a signal frequency 56, representing thedetected fundamental frequency of the power system signal. This signalfrequency 56 may be fed to the 1-bit FLL/PLL 32 to seed the signalfrequency value in the FLL/PLL. In return, the 1-bit FLL/PLL 32 mayprovide a frequency correction signal 57, which the transform processor50 may use to centre the bins of the transform operation so as to tunethe transform to the exact signal frequency. In some cases, thefrequency correction signal 57 may be the actual frequency signalmeasured by the FLL.

A spectral selector 54 may be configured to receive the transform domainsignal 52 and select particular components. The selected components maybe, for example, those at the power system fundamental frequency and, insome cases, harmonics of the fundamental frequency. The spectralselector 54 may have a model or algorithm for identifying “significant”components for selection from the transform domain signal. In someinstances, it may be a predefined model. In some cases, it may beadaptive and responsive to changes in the magnitude of components. Thespectral selector 54 may output the selected components as a fundamentalspectral components signal 58. The spectral selector 54 mayalternatively or also output a harmonics signal 60. The harmonics signal60 may include spectral data for harmonic components, but notnecessarily the fundamental power system frequency component.

The selected components output as the fundamental spectral componentssignal 58 are then passed through an inverse transform processor 62. Theinverse transform processor 62 converts the selected components back toa time-domain signal 64 containing the selected components. Thetime-domain signal 64 containing the selected components is thensubtracted from the 1-bit DS bitstream 14. In the embodiment shown inFIG. 4, the subtraction may be implemented as a 1-bit substractor forsubtracting 1-bit signals. In some cases, the time-domain signal 64 maybe converted from a multibit word signal to a 1-bit signal for thesubtraction. In yet other embodiments, the input DS bitstream 14 may beconverted to a multibit word signal and the subtraction may beimplemented as a multibit word subtractor.

In yet another embodiment, the subtraction may be implemented as asubtraction of the fundamental spectral components signal 58 from thetransform domain signal 52. The resulting signal, which is a transformdomain transients signal, is inverse transformed through the inversetransform processor 62 and the output of that process is the residualsignal 44. This embodiment eliminates time domain manipulation. Thesuccessful implementation of this embodiment may be partly dependentupon the DWT/IDWT pair used.

The result of the subtraction is the removal of the selected componentsfrom the bitstream 14, leaving a residual signal 44. The residual signal44 contains the high frequency noise components and other artifacts fromthe bitstream 14, including any transients or other features. A powerdetector 66 may be used to identify whether any transients are likelypresent in the residual signal 44. The power detector 66 may attempt toidentify brief but significant changes in power within the spectrum. Insome instances the power detector 66 may receive data from the transformprocessor 52 (not shown). The power detector 66 may output the transientdetect signal 46. In some implementations, the transient detect signalmay trigger the capture and reporting of the residual data in theresidual signal 44. Otherwise, the residual signal 44 may be discardedor temporarily stored for later analysis, if desired.

The 1-bit FLL/PLL 32 may supply phase information 74 to a phase jumpdetector 70. The phase jump detector 70 also receives the 1-bitbitstream 14 and produces a phase jump detection signal 72 in the eventthat it determines there has been a phase change greater than apredefined threshold within a period of time. The phase jump detectionsignal 72 may also be input to the 1-bit FLL/PLL 32 to allow the 1-bitFLL/PLL 32 to make adjustments to avoid phase jump errors, such asadjusting the FLL/PLL filter constants. In one embodiment, the filterconstants may be adjusted so as to quickly achieve lock or re-lock andthen adjusted to reduce phase noise (phase measurement accuracy) bytightening the loop bandwidth once locked. In one example implementation(not shown), the phase jump detector 70 includes a transform operator,such as a discrete Hilbert transform, applied to the 1-bit DS bitstream14 and a comparator for comparing phase information from the 1-bitFLL/PLL 32 to phase data for the 1-bit DS bitstream 14 from thetransform operator.

As noted above, the phasor data, such as the frequency signal 49 andphase signal(s) 48, are obtained using the 1-bit FLL/PLL 32 operatingupon the unfiltered 1-bit DS bitstream 14. The 1-bit DS bitstream 14 istypically clocked at a high sampling frequency. In one example thesampling frequency is about 6 Mbit/s. To obtain accurate phasor data,the 1-bit FLL/PLL 32 is implemented using high-speed single-bitarithmetic. In one example embodiment, the 1-bit FLL/PLL 32 isimplemented using a direct digital synthesizer (DDS) (not shown). Inanother example embodiment, the 1-bit FLL/PLL 32 is implemented in a

Coordinate Rotation Digital Computer (CORDIC) based architecture. TheCORDIC architecture is advantageous in that it requires few gates andsimple arithmetic operations.

It will be recalled that CORDIC is useful in calculating the sine orcosine of an angle. In particular, CORDIC techniques can be used torealize the expressions:

x _(m) =K[x ₀ cos(z ₀)−y ₀ sin(z ₀)]  (1)

y _(m) =K[y ₀ cos(z ₀)+x ₀ sin(z ₀)]  (2)

If y₀ is set to zero (which means x₀ defines a vector on the x-axis, aswill be explained below), then the equations become:

x _(m) =Kx ₀ cos(z ₀)  (3)

y _(m) =Kx ₀ sin(z ₀)  (4)

In the above expressions, x₀ and y₀ are the Cartesian coordinates of theinput signal or vector, z₀ is an angle that is signed ±1 depending onthe direction of rotation, and K is a constant. The effect is therotation (and scaling by K) of the input vector r₀ at coordinates x₀,y₀, by the angle z₀ to new coordinates x_(m), y_(m). The implementationof the CORDIC is the iterative rotation of the vector by progressivelysmaller angles until z₀ is approached with the required precision,meaning the absolute value of z_(m) is less than the required precisionin angle. An advantage of the CORDIC is that if the rotation anglesz_(i) are restricted such that tan(z_(i))=±2^(i), then the rotations canbe effected using shift and add operations. Note that m represents thenumber of stages or iterations.

Reference is now made to FIG. 5, which shows a simplified block diagramof a CORDIC-based implementation of the 1-bit FLL/PLL 32. One of theinput signals serves as a reference signal x_(r)(t), and the othersignals (seven other signals, in a three-phase four-wire system) aredesignated as phase signals x_(p)(t). A fundamental frequencymeasurement is made with regard to the reference signal x_(r)(t), whilephase offsets are determined for the phase signals x_(p)(t). For ease ofillustration, only one phase signal x_(p)(t) is shown in FIG. 5.

The DS modulators 12 convert the input signals to 1-bit DS bitstreams14. The 1-bit DS bitstream 14 for reference signal x_(r)(t) is input toa rotate CORDIC 102. The rotate CORDIC 102 receives an input angle z₀,which in this case is a ramp function produced by a phase accumulator104. The rotate CORDIC 102 outputs an in-phase digital word x_(m), foreach input bit x₀, wherein x_(m) is a multibit word of about 2m bits ofprecision. Further details of example implementations of the 1-bitrotate CORDIC 102 are provided below.

The output of the 1-bit rotate CORDIC 102 are the following two signals:

x _(m) =Kx ₀ cos(z ₀)  (5)

y _(m) =Kx ₀ sin(z ₀)  (6)

In this case, x₀ is the 1-bit DS bitstream, which is a DS bitstreamrepresenting the power system signal (ignoring for the purposes of thisexplanatory mathematics, any harmonics and noise).

It will also be noted that the phase ramp produced by the phaseaccumulator 104 of the 1-bit FLL/PLL 32 is driven by a frequencyregister 106 containing the measured power system fundamental frequency(this may initially be seeded to 60.0 Hz, but will then lock to theactual frequency). In other words, the angle z₀ is based upon the powersystem frequency found in x₀.

Accordingly, the output of the rotate CORDIC 102 are the signals:

x _(m) =K cos(z ₀)*a sin(ωt+φ)  (7)

y _(m) =K sin(z ₀)*a sin(ωt+φ)  (8)

It will be appreciated that this mixing results in a half amplitudedifference signal at z₀−(ωt+φ) and a half amplitude additive signal atz₀+(ωt+φ). As z₀ approaches cot, the difference signals are essentiallya pair of DC signals, whereas the additive signal is an AC signal.Accordingly, since we are interested in the difference signals, x_(m)and y_(m) are passed through low pass filters 108, 110 and the filtereddifference signals are input to a vector CORDIC 112.

The vector CORDIC 112 is similar to the rotate CORDIC 102, but insteadof rotating an input vector defined by coordinates to a new set ofcoordinates, the vector CORDIC 112 rotates the input vector to thex-axis and outputs the angle required to make that rotation occur. Theangle output z_(m) from the vector CORDIC 112 is given by:

z _(m) =z ₀′+tan⁻¹(y ₀ ′/x ₀′)  (9)

For clarity the input signals are labeled x₀′ and y₀′. The input z₀′ isan arbitrary constant angle which, in one embodiment is set to 0. Inanother embodiment, it may be set to π/4, for example if the ratio inthe arctangent was expected to lock at unity.

It will be recalled that the low pass filtered input signals to thevector CORDIC 112 are the (x,y) DC projection of the input signal ontothe reference oscillator. The input signal and the reference oscillatorare sinusoidal in nature. Accordingly the phase offsets x₀′ and y₀′, maybe considered like a cosine function and a sine function, respectively.Their ratio reduces to a tangent function. As a result Equation (9) maybecome:

z _(m) =z ₀ ′+z ₀−(ωt+φ)  (10)

In other words, the output of the vector CORDIC 112 is a phase errorsignal 114. The phase error signal is input to the frequency register106 to adjust the fundamental frequency contained therein and lock tothe power system frequency.

As noted previously, the frequency register 106 feeds the fundamentalfrequency to the phase accumulator 104 through an additive loop to forma numerically controlled oscillator that produces the phase ramp tosupply z₀. A time correction signal 116 may be added to the numericallycontrolled oscillator to correct for errors in the local oscillators.The time correction signal 116 may be derived from external timesources, such as GPS or an IRIG-B signal. The time correction signal 116may be added to the input to the phase accumulator 104, i.e. the stepsize input to the accumulator 104, or may be input directly to thefrequency register 106. In yet another embodiment, the time correctionsignal 116 plus 1(unity) may be multiplied by the output of thefrequency register 106 before it is used as the input step size to theaccumulator 104.

It will be appreciated that this portion of the 1-bit FLL/PLL 32provides a frequency lock to the fundamental frequency of the powersystem, which is found in the frequency register 106 once it has locked.The rotate CORDIC 102 operates on the 1-bit input signal producing aoutput word of about 2m for each bit of the input signal x₀. In twoexample embodiments, the m-stage rotate CORDIC 102 may be implemented byclocking the CORDIC at m times the sampling frequency f_(s), or byunrolling the CORDIC and clocking it at about the sampling frequency butaccepting an m bit delay. The latter example will be shown in greaterdetail below, but the present application is not limited to an unrolledconfiguration.

Referring still to FIG. 5, the phase signal x_(p)(t) is input to asimilar circuit. In particular, the phase signal x_(p)(t) serves as the1-bit input signal x₀ to a rotate CORDIC 122. The rotate CORDIC 122receives the same ramp function z₀ from phase accumulator 104, but phaseadjusted by the value from a phase offset register 128. The output ofthe rotate CORDIC 122 is low pass filtered through LPFs 125 and 124 andthe filtered difference signals are input to a vector CORDIC 126. Thevector CORDIC 126 supplies phase offset correct signal 130. The phaseoffset correction signal 130 is fed to the phase offset register 128,which contains the phase difference between the phase signal x_(p)(t)and the reference signal x_(r)(t).

It will be understood from the present description that the vectorCORDICs 112, 126 need not operate at the same speed as the rotateCORDICs 102, 122. In fact, in some example embodiments, the hardware forimplementing the vector CORDICs 112, 126 may be shared amongst the inputsignals, meaning only a single hardware implementation of a vectorCORDIC 112, 126 may be required. Additional hardware sharing may bepossible in other implementations, depending on the speed of thehardware clocking and the sampling frequency f_(s).

In one embodiment, the vector CORDICs 112, 126 may be replaced byalternative circuitry for determining the phase difference based on theinput difference signals. For example, in one alternative embodiment thevector CORDIC 112 may be replaced with a division and a piece-wiselinear interpolation of arctangent. The present application is notlimited to the use of a vector CORDIC for this function. Nevertheless,it will be appreciated that the elimination of a division through use ofthe vector CORDIC 112 can be advantageous in some implementations.

Reference is now made to FIG. 6, which diagrammatically illustrates oneexample implementation of a 1-bit rotate CORDIC 200. In this example,only the x-side of the CORDIC 200 is illustrated for clarity. Asdiscussed above, the rotate CORDIC 200 has m stages and results in anoutput word having about 2m bits of precision for each input bit. Thisenables significantly precise frequency and phase locking andmeasurement using unfiltered 1-bit DS signals. As will be shown below,the implementation, in one embodiment, can be efficiently realized inhardware using shift and add operations.

The input to the CORDIC 200 is a bit from the 1-bit DS signal 14 (FIG.5), which is shown as x₀. The value for x₁ depends upon y₀ and z₀. Inparticular, the value of any x_(i) is given by:

x _(i+1) =x _(i) −y _(i) ·d _(i)·2^(−i),  (11)

-   -   where d_(i)=−1 if z_(i)<0 and +1 otherwise

Each z_(i) is calculated as:

z _(i+i) =z _(i) ·d _(i)·tan⁻¹(2^(−i))  (12)

Using a look-up table for the term −d_(i)·tan⁻¹(2^(−i)), the remainingoperations for realizing these values are additions and shifts.Moreover, because the input is a single bit in the first stage, theprocess is hardware efficient because a the precision length grows withthe stages, meaning a full output word need not be carried in each stageof the calculations.

The implementation of the rotate CORDIC 200 shown in FIG. 6 is anunrolled CORDIC. The value x₀ may be notionally considered a sign bit insome sense. Similarly the value y₀ (which is set to zero), may beconsidered a signed zero.

The rotate CORDIC 200 is thus implemented using simple binary additionand shift operations. Each of the m stages of the CORDIC 200 includesbit-shifting the value from the parallel y-side of the CORDIC by apredetermined number of places, and adding or subtracting it from thex_(i) value from that stage depending on whether z_(i) is below zero ornot. In a parallel operation, the value of z_(i) is determined at eachstage based upon the previous value and look-up table value for the term−d_(i)·tan⁻¹(2^(−i)). The look-up table value is fixed at each stage andcan be hardwired if desired.

It will be appreciated that the operations involved in the CORDIC 200are relatively straightforward to implement using binary add and shiftoperations. In one embodiment, the CORDIC 200 is implemented using afield programmable gate array. In one such embodiment, the rotate CORDIC200 may be implemented using only about m²−m+2 adders in total for the mstages of x and y calculations to produce an output word of about 2mbits of precision.

It will also be appreciated that the above-described implementation ofthe one-bit rotate CORDIC 200 carries precision as the word size grows,rather than maintaining full word precision at every stage. Accordingly,since the input is a single bit at the first stage, the CORDIC onlyneeds to maintain single bit precision at that stage.

It will be understood that the foregoing power measurement device may beimplemented partly in hardware and partly in software. In someembodiments, the implementation may include one or more fieldprogrammable gate arrays (FPGA). In some embodiments, the implementationmay include one or more microprocessors or microcontrollers. In someembodiments, the implementation may include one or moreapplication-specific integrated circuits (ASIC). The selection ofparticular hardware components may be based upon cost, speed, operatingenvironment, etc. The selection and programming of such components willbe within the understanding of a person of ordinary skill in the arthaving regard to the detailed description provided herein.

In yet a further aspect, the present application discloses acomputer-readable medium having stored thereon computer-executableinstructions which, when executed by a processor, configure theprocessor to execute any one or more of the methods described above.

Certain adaptations and modifications of the described embodiments canbe made. Therefore, the above discussed embodiments are considered to beillustrative and not restrictive.

What is claimed is:
 1. A method of measuring power systemcharacteristics, the power system having a system frequency and one ormore phases, the method comprising: sampling one of voltage or currentof the power system to produce a 1-bit delta-sigma modulated bitstream;generating in-phase and quadrature difference signals from the 1-bitdelta-sigma bitstream using a 1-bit rotate CORDIC receiving a phase rampsignal, the difference signals each having a multi-bit word for each bitof the 1-bit delta-sigma signal, wherein the phase ramp signal has aperiodicity based upon a frequency value; and generating a phase errorsignal based upon a difference between the difference signals, whereinthe difference indicates an error between a phase of the phase rampsignal and the phase of the system frequency contained within the 1-bitdelta-sigma signal; and adjusting the frequency value to lock it to thesystem frequency based upon the phase error signal.
 2. The methodclaimed in claim 1, wherein the 1-bit rotate CORDIC receives the 1-bitdelta-sigma signal from a delta-sigma modulator without any low-passfiltering.
 3. The method claimed in claim 1, further including low passfiltering outputs of the 1-bit rotate CORDIC to produce the differencesignals.
 4. The method claimed in claim 1, further including samplingone of voltage and current on one or more phases of the power systemthereby producing one or more additional 1-bit delta-sigma signals, andfurther comprising generating in-phase and quadrature difference signalsfor each of the one or more additional 1-bit delta-sigma bitstream usingrespective one or more 1-bit rotate CORDICs and producing respectiveadditional in-phase and quadrature difference signals.
 5. The methodclaimed in claim 1, wherein generating the phase error signal comprisesusing a vector CORDIC.
 6. The method claimed in claim 1, furthercomprising transmitting the frequency value to a remote locationtogether with a time stamp.
 7. The method claimed in claim 1, furthercomprising determining a RMS value for the voltage or current based uponthe 1-bit delta-sigma signal.
 8. A power measurement device formeasuring phase and frequency in multi-phase power system, the powersystem having a system frequency, the device comprising: a plurality ofdelta-sigma modulators each measuring one of voltage or current on oneof the phases in the multi-phase power system and outputting a 1-bitdelta-sigma signal; a phase accumulator configured to produce a phaseramp signal having a periodicity determined by a frequency value; a1-bit rotate CORDIC for each delta-sigma modulator, wherein each 1-bitrotate CORDIC receives the phase ramp signal and a respective one of the1-bit delta-sigma signals and outputs an in-phase difference signal anda quadrature-phase difference signal, the difference signals each havinga multi-bit word for each bit of the 1-bit delta-sigma signal; and aphase error calculator for each 1-bit rotate CORDIC to receive thedifference signals from that 1-bit rotate CORDIC and to output a phaseerror signal based upon the difference between a phase of the phase rampsignal and the phase of the respective one of the 1-bit delta-sigmasignals, wherein one of the phase error calculators corrects thefrequency value using its phase error signal to lock it to the systemfrequency, and wherein the other of the phase error calculators correctsa respective phase offset value measured for its respective one of the1-bit delta-sigma signals using its respective phase error signal. 9.The power measurement device claimed in claim 8, wherein the same phaseramp signal is received by each of the 1-bit rotate CORDICs.
 10. Thepower measurement device claimed in claim 8, wherein the phase errorcalculators comprise vector CORDICs.
 11. The power measurement deviceclaimed in claim 8, wherein the 1-bit rotate CORDICs comprise m stageCORDICs and the multi-bit word is 2m±1 bits for every input bit of the1-bit delta-sigma signal.
 12. The power measurement device claimed inclaim 8, further comprising a register to store the frequency value andrespective registers to store the phase offset values.
 13. The powermeasurement device claimed in claim 8, wherein the phase accumulatorreceives an input based upon its output, the frequency value and a timecorrection signal.
 14. The power measurement device claimed in claim 13,wherein the input comprises the phase accumulator output plus a stepsize based on the frequency value adjusted by the time correctionsignal, clocked based on a local oscillator, and wherein the timecorrection signal corrects for error in the local oscillator.
 15. Amethod of measuring phase and frequency in multi-phase power system, thepower system having a system frequency, the method comprising: measuringone of voltage or current on each one of the phases in the multi-phasepower system and delta-sigma modulating each of the measurements tooutput 1-bit delta-sigma signals; generating a phase ramp signal using aphase accumulator, the phase ramp signal having a periodicity determinedby a frequency value; for each of the 1-bit delta-sigma signals,producing an in-phase difference signal and a quadrature-phasedifference signal using a respective 1-bit rotate CORDIC, wherein each1-bit rotate CORDIC receives the phase ramp signal and its respectiveone of the 1-bit delta-sigma signals, the difference signals each havinga multi-bit word for each bit of the 1-bit delta-sigma signal; for eachpair of difference signals, generating a phase error signal based uponthe difference between a phase of the phase ramp signal and the phase ofthe respective one of the 1-bit delta-sigma signals; correcting thefrequency value to lock it to the system frequency using one of thephase error signals; and for each of the other phase error signals,correcting a respective phase offset value measured for its respectiveone of the 1-bit delta-sigma signals.
 16. The method claimed in claim15, wherein the same phase ramp signal is received by each of the 1-bitrotate CORDICs.
 17. The method claimed in claim 15, wherein the 1-bitrotate CORDICs comprise m stage CORDICs and wherein producing thein-phase difference signal or the quadrature-phase difference signalcomprises producing a multi-bit word of 2m±1 bits for every input bit ofthe 1-bit delta-sigma signal.
 18. The method claimed in claim 15,further comprising storing the frequency value in a register and storingthe phase offset values in respective registers.
 19. The method claimedin claim 15, wherein generating the phase ramp signal comprisesreceiving an input based upon a feedback phase ramp signal, thefrequency value and a time correction signal.
 20. The method claimed inclaim 19, wherein the input comprises the phase accumulator output plusa step size based on the frequency value adjusted by the time correctionsignal, clocked based on a local oscillator, and wherein the timecorrection signal corrects for error in the local oscillator.